Cognitive radio refers to a radio device which can intelligently detect which communication channels are in use by primary users and which are not, and move into vacant channels while avoiding occupied ones.
An important function of cognitive radios is spectrum sensing, generally referring to detecting unused spectrum. Cognitive radios attempt to sense “spectrum holes”. A spectrum hole is a frequency range, where the absence of primary users has been determined. Primary users are for example TV stations, wireless microphones or cellular systems. By detecting particular spectrum holes and exploiting them rapidly, cognitive radios can significantly improve spectrum utilization. Detecting the absence of primary users is a difficult task and a single detector may make errors when determining whether the spectrum is primary free or not.
One sensing technique is so-called distributed or co-operative spectrum sensing, where sensing results from more than one secondary device are combined. The combination of sensing results enables better detection probability. In ideal case, a cognitive radio receives detection results from all nearby cognitive radios. In practice, this may be impractical due to large amount of signalling. Thus, there is a need for optimizing the use of resources for co-operative spectrum sensing.